Multiple sclerosis (MS) is a chronic inflammatory disease characterized by demyelination and degeneration of axons in the central nervous system (CNS). Compelling evidence suggests that breakdown of the blood-brain barrier (BBB) and angiogenic remodeling occur at an early stage of MS as well as in the animal model of MS, experimental autoimmune encephalomyelitis (EAE), and is central to the initiation and maintenance of disease pathogenesis by affording leukocyte infiltration into the brain parenchyma. This vascular remodeling, in turn, is strongly influenced by the interaction between extracellular matrix (ECM) proteins and their endothelial integrin cell surface receptors. In particular, the ?5?1 integrin and its ligand fibronectin are strongly upregulated on remodeling cerebral vessels in animal models of ischemic stroke and MS, and transgenic mice lacking this receptor in endothelial cells (?5-EC-KO mice) show delayed and reduced angiogenic remodeling in response to hypoxia. Furthermore, our recent studies in an experimental stroke model showed that ?5-EC-KO mice are profoundly resistant to BBB breakdown, resulting in dramatic reductions in size of ischemic infarct. Pharmacological blockade of ?5?1 integrin in wild-type (WT) mice achieved similar protection. As BBB breakdown and angiogenesis occur at an early stage of MS and EAE, and current evidence suggests that the ?5?1 integrin is an important trigger of cerebrovascular remodeling, we hypothesize that inhibition of endothelial ?5?1 integrin stabilizes the BBB and reduces leukocyte infiltration in demyelinating disease. In support of this hypothesis, new preliminary results suggest that pharmacological blockade of ?5?1 integrin in cultured WT brain endothelial cells stabilizes their barrier properties in presece of the barrier-disrupting inflammatory cytokine TNF-?. These studies also suggested that protection may be a result of increased expression of claudin-5, a tight junction protein and critical component of the BBB. Armed with these results, we propose the following specific aims: (1) determine whether genetic deletion or pharmacological blockade of ?5?1 integrin on endothelial cells stabilizes the BBB, resulting in reduced neuroinflammation and demyelination in the EAE model, and 2) determine the molecular mechanism whereby ?5?1 integrin inhibition promotes BBB integrity and subsequent resistance to EAE. We expect to demonstrate that inhibition of ?5?1 integrin in endothelial cells confers robust resistance to EAE by increasing BBB integrity through stabilization of tight junction proteins and suppression of the leukocyte- homing adhesion molecules ICAM-1 and VCAM-1. Successful completion of these studies will further our goal of developing endothelial ?5?1 integrin as a novel MS therapeutic target.